There are positive and negative charges. Look at is this way a charge attracts a positive charge. On the other hand, when a charge is brought near a distributed charge, high is your hair for this, the positive charge attracts the negative charge so opposite charge concentration increases in the hair. So, when the same type of charge is in the hair, the hair stands up.
Okay, so Your hair holds a positive or negative charge, then a balloon holds a charge different from you hair charge. So when a positive and a negative come together they make your hair rise
